This invention relates to a process for metallizing a glass surface usable for forming circuits on, for example, crystalline phase-containing glass substrates, crystallized enameled substrates, ceramic substrates coated with crystalline phase-containing glass, and producing printed wiring boards.
In order to metallize crystalline phase-containing glass (hereinafter referred to as "crystallized glass") surfaces, particularly to form circuits in the production of printed circuit boards, there have been known (1) a thick film process wherein a wiring pattern is formed on a substrate with a metallic paste by firing, and (2) a thin film process wherein a wiring pattern is formed on a substrate by sputtering or chemical vapor deposition (CVD). But the thick film process (1) has problems in that since a circuit is formed by a printing method, it is difficult to form wiring (circuit formation) on inner walls of through-holes of a substrate or curved portions at ends of a substrate, and since the firing temperature is as high as higher than 800.degree. C., a noble metal paste should be used in order to prevent oxidation, which results in making the production cost high. On the other hand, the thin film process (2) has problems in that it is difficult to form wiring (circuit formation) on inner walls of through-holes of a substrate or curved portions at ends of a substrate like the thick film process, this process is not suitable for mass production, and it is difficult to make the metal film thickness large, etc.
In order to solve such problems, it is proposed to conduct electroless plating on crystallized glass surfaces. For example, Japanese Patent Unexamined Publication Nos. 53-5438 and 60-195078 disclose processes wherein crystallized glass surfaces are roughened by hydrofluoric acid (the former patent) and molten NaOH (the latter patent). But when hydrofluoric acid or molten NaOH is used, since these substances are too strong in corrosive force, a crystallized glass surface is dissolved irrespective of a crystalline phase or non-crystalline phase. Thus, it is difficult to control the formation of relief on the roughened surface. Further, since a weak layer is formed near the surface, an electroless plating layer formed later is peeled off together with the weak layer. Thus, it is difficult to obtain stable adhesive strength. In addition, hydrofluoric acid and molten NaOH are dangerous for handling.